Lead pencil and method of manufacture



3,086,903 LEAD FENCE. AND METHOD OF MANUFACTURE Harold Grossrnan, UpperMontclair, Ni, assignor to I-lassenfeld Eros, inca, Central Falls, Ri acorporation of Rhode island N Drawing. Filed Apr. 19, 1960, Ser. No.23,149 17 Claims. (Cl. 156-273) The invention relates to improvements inmethods for manufacturing lead pencils, and the resultant article. Thisapplication is a continuation-in-part of my pending application SerialNo. 719,706, filed March 7, 1958, now abancloned.

Leads for wood-encased pencils comprise an extruded mixture of clay andgraphite which is baked or sintered at a high temperature, and thenimpregnated or coated with a grease, wax, oil, or mixture of two or moreof such materials to furnish the desired smooth-writing quality. Thegreasy surface character of the lead makes it diflicult to adhere to thesurrounding wood sheath. Nevertheless, firm adherence between the leadand the wood is necessary to prevent breakage at the feathered orsharpened writing end, to prevent movement of the lead within the woodsheath, etc. The grooved wood slats are coated or impregnated to furnishadded strength, improved resistance to breakage upon sharpening, butbonding the wood slats to each other has not presented any problem.Bonding the greasy lead to the wood, however, has been the subject ofintensive research efliort for many years.

To the best of my knowledge, it has been necessary to subject the leadto a preliminary treatment of some kind to condition it for adherence tothe wood. Essentially, these preliminary conditioning treatments haveinvolved the modification of the greasy surface in some fashion torender the surface suitable for bonding.

One of the early methods for conditioning the greasy lead to prepare itfor adherence to the wood is disclosed by Gonzalez, Patent No.1,892,508, December 27, 1932, and involves immersion of the leads insulfuric acid, followed by immersion in a solution of a suitable salt,such as calcium chloride, to precipitate the salt onto the lead. Theinsoluble precipitate formed on the surface of the lead permitsadherence to the wood with the usual water soluble glue.

As disclosed in my Patent 1,958,194, January 1, 1935, the greasy lead isprepared for bonding to the wood by treatment with chromic acid,followed by washing in water and neutralization of traces of the chromicacid.

As disclosed in Chesler 2,116,217, May 3, 1938, the greasy lead istreated with a wetting or penetrating agent, such as a sulfonated oil,to provide a surface which is miscible with the water soluble glue usedto adhere the wood slats to each other and to the thus treated lead.

Herstein 2,098,452, November 9, 1935, forms crystals of a detergent salton the surface of the greasy lead, such crystal structure affordingmechanical means for keying the thus treated lead to the wood by a watersoluble glue.

The surface of the greasy lead has been variously roughened or pitted topermit mechanical keying to the wood by the glue or adhesive. Suchsurface roughening has been accomplished by a knurled tool or by sandblasting, as disclosed by Ferst 2,131,657, September 27, 1938; byincluding a gas liberating agent in the composition comprising the leadwriting element, the gas, when liberated, providing a pitted surface, asdisclosed by Zuckert 2,190,518; by subjecting the greasy lead to anelectric arcing action, as shown by Best 2,229,633, January 28, 1941;and by subjecting the greasy leads to an electrochemical action, asdisclosed by McKee 2,228,772, January 14, 1941.

3,985,903 Patented Apr. 23, 1963 ice More recently, and as disclosed byGrieco 2,515,118, July 11, 1950, an adhesive pattern is printed onto thelead prior to impregnation with the essential greasy substance. Theadhesive pattern printed lead is then impregnated with a greasysubstance. The resulting discontinuous greasy surface, broken up by theprinted adhesive pattern, facilitates bonding such conditioned lead tothe wood sheath members and the wood sheath members to each other by thesame kind of adhesive used to print the pattern on the leads; forexample, a vinyl resin emulsion, or other types of adhesives.

It will be apparent that the prior art necessity to resort to apreliminary conditioning of the lead, whether the lead is treated afterit has been grease impregnated, or specially treated, as by the patternprinting, before grease impregnation, constitutes an additionaloperation or operations, and adds to the cost of manufacturing theproduct.

Moreover, even with the leads preliminarily treated for the purpose ofenabling them to be bonded to the wood, the operation of assembling andadhering the leads within the grooved wood slats has been a bottleneckin the process of manufacture. It has been the practice to apply a watersoluble animal glue, or any other suitable adhesive, such as a wateremulsion of a synthetic resin to the grooved sides of a pair of slats,lay the leads in the grooves of one of the wet coated slats, place theother wet coated slat thereon to form a so-called block, take aplurality of the blocks, anywhere from 40 to 80, place them underpressure in a large clamp, and then put the clamped blocks in a dryingoven for a period of approximately six (6) to eight (8) hours in orderto set the wet glue line. The unduly long period of time required to dryand set the adhesive to adhere the elements together is in markedcontrast to the prior and subsequent rapid operations of grooving theslats, and cutting the blocks and shaping to form the individualpencils. The inordinate amount of time required to assemble and adherethe leads within the blocks has prevented the realization of astraight-line or continuous method of pencil manufacture.

A primary object of the invention is to provide a method ofmanufacturing wood-encased lead pencils by adhering the leads directlyto the wood sheath members or slats, with the leads in their usualgreasy condition, unmodified by a preliminary treatment of any kind,either after or before grease impregnation, thereby providing a novelproduct wherein the greasy lead is adhesively united directly to thewood sheath without any modification of the leads greasy surface otherthan may result from the eifect of the adhesive itself, which alsounites the wood sheath members.

Another important object of the invention is to provide a continuous, orstraight-line method of pencil manufacture in the sense that the timeinterval required to firmly bond the leads within the block or to thewood slats is accomplished substantially as rapidly as the previousoperation of grooving the slats and the subsequent operations of cuttingthe block into individual pencils and suitably shaping such cut units.

These, and other objects and advantages of the invention, will beapparent from the following detailed description of a preferredembodiment of the invention and several modifications thereof.

In accordance with a preferred form of the invention, a pair of groovedwood slats are coated on their grooved sides with a vinyl resin compoundin a suitable vehicle or carrier; that is to say, a water emulsion or asolvent solution of the resin. The resin emulsion or solution is appliedby brushing or spraying, and the coatings are applied within the groovesas well as on the intervening flat surfaces. The water or solvent isimmediately and rapidly driven oif by applying heat to the coatings toform a thin, substantially dry film of the vinyl resin adhesive on eachof the grooved slats. Although any suitable heat source may be used, itis preferred to use infra-red lamps. Depending upon the amount ofplasticizer present, the temperatures of the vinyl resin films areapproximately 100 to 200 C. The leads are placed in the grooves of oneof the slats, and while the adhesive films are still hot from the heatof drying, the other slat is placed thereon and the block is subjectedto pressure or clamped. Within a period as short as fifteen (15)seconds, the block may be removed from the clamp, and the leads arefirmly adhered to the wood, and, of course, the wood slats are alsofirmly bonded to each other. And this is accomplished with greaseimpregnated leads of the usual variety, which are in no way conditionedto change their continuous greasy surface characteristics prior to beingplaced in the grooves of a slat.

Instead of drying the wet coating on the grooved sides of the wood slatsbefore assembling the Wood slats with the leads, the slats, with thecoatings thereon still wet, may be assembled with the greasy leads inthe mating grooves. The coatings are then dried in the absence of anypressure upon the assembly. The assembly is subjected to dielectric orhigh frequency heating to cause the vehicle or carrier for the vinylresin adhesive to be driven ofi. The assembly having the dry line ofadhesive is then subjected to pressure in the presence of heat.Additional heating is unnecessary if pressure is applied to the assemblywhile the dry vinyl resin adhesive film is still hot from the heat ofdrying.

The preferred vinyl resin adhesive coating composition is a wateremulsion of a plasticized vinyl acetate. From the standpoint of thedegree of adhesion between the greasy lead and the wood, coupled withthe most rapid method of processing and least expense, I have obtainedthe best results by using a water emulsion of polyvinyl acetate and aplasticizer known as Hercoflex 900, made by the Hercules Powder Company,which is understood to be a benzoic acid derivative. Examples of benzoicacid derivatives are ethylene glycol dibenzoates, and the polyethyleneglycol dibenzoates. The solids content of the emulsion is preferablyapproximately 50%, with a resin content of 80 to 95%, and a plasticizercontent of from 5 to 20% by weight. Other known plasticizers, such as apht'halic acid derivative, a glycol derivative, an abietic acidderivative, or an adipic acid derivative may be used. While a wateremulsion of the polyvinyl acetate is preferred, a solvent solution mayalso be used, suitable solvents being alcohol, a chlorinatedhydrocarbon, a fatty acid ester, an aromatic hydrocarbon, or a ketone.

The adhesive coating composition may be in the form of a solventsolution of polyvinyl chloride, or a vinyl chloride acetate copolymer,suitably plasticized.

I am unable to definitely account for the phenomenon which enables theachievement of the unusually high degree of adhesion between the greasy,untreated lead and the wood with the plasticized polyvinyl adhesive,when such adhesive is used in the manner as above described. Myexperimentation has indicated that when an emulsion or solution of thesame vinyl composition is used in the usual manner; that is to say,applying pressure to and drying the assembly or block of greasy leads inthe grooved woods slats with the line of adhesive in the usual wetcondition, the result is poor or no adhesion, regardless of the amountof pressure, and however long the block is clamped and dried. On theother hand, when the adhesive coating is in substantially dry conditionprior to clamping or applying pressure -to the block, adhesion takesplace, in the presence of heat, despite the greasy surface character ofthe lead. Then, too, the vinyl compounds apparently are peculiarlyconstituted to afford a satisfactory bond to greasy lead, when used inthe manner described. Experimentation with a variety of otherthermoplastic adhes ve coatings, even when-used in the'exact same way asherem- 4 before described, has resulted in poor adhesion. Besides theexcellent adhesion furnished by the plasticized polyvinyl compounds whenused in the manner described, such compounds furnish an adhesive linewhich does not unduly dull the cutters when the blocks are cut into theindividual pencil units.

The method as hereinbefore described in detail, produces a wood-encasedpencil of top quality from the standpoint of the high measure ofadhesion between the greasy lead and the wood and, of course, the Woodto wood. The method of manufacture is economically advantageous, becausethe greasy leads do not require a preliminary or special treatment tocondition them for bonding to the Wood. Also, the rapidity with whichthe grooved Wood slats and the greasy leads may be satisfactorilyadhered eliminates the inordinately long period of time heretoforerequired to clamp and dry the blocks, thereby permitting a straight-lineor continuous method of manufacturing pencils.

While the particular method hereinbefore described is preferred,numerous modifications may :be made to realize some, if not all, of themany advantages over the prior art. For example, while rapidity ofprocessing is best realized by utilizing the same heat of drying theplasticized polyvinyl coatings to adhere the greasy leads to the woodand the wood slats to each other, I have found that a product ofsubstantially equal quality is obtained by first drying the adhesivecoatings on the slats to room temperature, and then activating the driedadhesive coatings by applying heat thereto just prior to forming theblock, or by applying heat with the pressure applied to the block. Sincein this modified form of the invention, the heat of drying is not usedto laminate the elements, the coatings may be initially dried withoutheat, or by the circulation of air.

While the best results are obtained by applying the plasticizedpolyvinyl emulsion or solution to both grooved slats, it is within thescope of the invention to apply such adhesive coating to only one of theslats before drying, leading, forming the block and applying pressurethereto in the presence of heat. Also, the greasy leads may be placed inthe grooves of one of the slats before applying the plasticizedpolyvinyl coatings to both slats, drying and assembling. Also, while itis most convenient to apply the vinyl resin as a wet coating, the resinmay be applied as a dry powder and fused by heat to form the continuousadhesive film or films on one or both grooved sides of the slats.

While the invention has been specifically described in connection withgreasy leads of the black element type, itis also withinthe purview ofthe invention to use leads of the colored type. Colored leads, whichgenerally comprise a suitable pigment or dye, a wax, and a water solublegum are also difiicult to adhere to wood, because of their waxy orgreasy-like surface character. The described precedure satisfactorilyadheres colored leads to the wood sheath members, and does not requireany preliminary treatment of such leads. In processing colored leads,the plasticizer content is increased so that there are approximatelyequal parts, by weight, of the vinyl resin and the plasticizer.

The term greasy lead as used in the claims is intended to include boththe black and colored writing lead elements, which have a continuousgreasy or waxy surface character, unmodified by any treatment prior toassembly With'the slats to change their usual unbroken greasy or waxysurface character for the purpose of obtaining adhesion.

It is believed that the numerous advantages of the invention ashereinbefore described, will be apparent from the foregoing detaileddescription. While a preferred embodiment of the invention has beendescribed, and several modifications have been indicated, it will beapparent that other changes are contemplated within the spirit and scopeof the invention, as sought to be defined in the following claims.

I claim:

1. A method of making wood-encased lead pencils comprising providing asubstantially dry vinyl resin adhesive film within the grooves and uponthe adjacent flat areas of a grooved wood slat which is assembled with asecond grooved slat and with greasy leads disposed in the matinggrooves, and applying pressure to the assembly in the presence of heatto directly adhere the greasy leads to a wood slat and the wood slats toeach other.

2. A method of making wood-encased lead pencils comprising applying awet coating of a vinyl resin within the grooves and upon the adjacentflat areas of each of a pair of grooved wood slats, disposing greasyleads in one of the slats, assembling the other slat therewith, andapplying pressure to the assembly in the presence of heat to directlyadhere the greasy leads to the wood slats and the wood slats to eachother, said coating being dried to provide a substantially dry vinylresin adhesive prior to the application of pressure.

3. A method of making wood-encased lead pencils as set forth in claim 2,wherein the substantially dry vinyl resin adhesive is deposited from anemulsion of plasticized polyvinyl acetate.

4. A method of making wood-encased lead pencils as set forth in claim 2,wherein the substantially dry vinyl resin adhesive is deposited from anemulsion of polyvinyl acetate plasticized with a benzoic acid derivativein the proportions of approximately 80 to 95 percent of the polyvinylacetate and 5 to 20 percent of the benzoic acid derivative, by weight.

5. A method of making wood-encased lead pencils comprising providing asubstantially dry vinyl resin adhesive film within the grooves and uponthe adjacent flat areas of a grooved wood slat, assembling the adhesivefilm coated slat with a second grooved slat and with greasy leadsdisposed in the mating grooves, and applying pressure to the assembly inthe presence of heat to directly adhere to the greasy leads to a woodslat and the Wood slats to each other.

6. A method of making wood-encased lead pencils comprising applying awet coating of a vinyl resin within the grooves and upon the adjacentflat areas of a grooved wood slat, drying the coating to form asubstantially dry vinyl resin adhesive film, assembling the adhesivefilm coated slat with a second grooved slat and with greasy leadsdisposed in the mating grooves, and applying pressure to the assembly inthe presence of heat to directly adhere the greasy leads to a wood saltand the wood slats to each other.

7. A method of making wood-encased lead pencils comprising applying awet coating of a vinyl resin within the grooves and upon the adjacentflat areas of each of a pair of grooved wood slats, drying the coatingsto form a substantially dry vinyl resin adhesive film on each of theslats, disposing greasy leads in one of the slats, placing the otherslat thereon, and applying pressure to the assembly in the presence ofheat to directly adhere the greasy leads to the Wood slats and the woodslats to each other.

8. A method of making wood-encased lead pencils as set forth in claim 7,wherein the substantially dry vinyl resin adhesive film on each of theslats is deposited from an emulsion of plasticized polyvinyl acetate.

9. A method of making wood-encased lead pencils as set forth in claim 7,wherein the substantially dry vinyl resin adhesive film on each of theslats is deposited from an emulsion of polyvinyl acetate plasticizedwith a benzoic acid derivative in the proportions of approximately topercent of the polyvinyl acetate and 5 to 20 percent of the benzoic acidderivative, by weight.

10. A method of making wood-encased lead pencils comprising applying awet coating of a vinyl resin within the grooves and upon the adjacentflat areas of each of a pair of grooved wood slats, applying heat to thecoated slats to form a substantially dry vinyl resin adhesive film oneach of the slats and, while the coatings are still hot from the heat ofdrying, placing the other slat thereon and applying pressure to theassembly to directly adhere the greasy leads to the wood slats and thewood slats to each other.

11. A method of making wood-encased lead pencils as set forth in claim10, wherein the dry vinyl resin adhesive film on each of the slats isdeposited from an emulsion of plasticized polyvinyl acetate.

12. A method of making wood-encased lead pencils as set forth in claim10, wherein the substantially dry vinyl resin adhesive film on each ofthe slats is deposited from an emulsion of polyvinyl acetate plasticizedwith a benzoic acid derivative in the proportions of approximately 80 to95 percent of the polyvinyl acetate and 5 to 20 percent of the benzoicacid derivative, by Weight.

13. A method of making wood-encased lead pencils comprising applying awet coating of a vinyl resin within the grooves and upon the adjacentfiat areas of a grooved wood slat, assembling the coated slat with asecond grooved slat and with greasy leads disposed in the matinggrooves, drying the coating in the absence of pressure upon theassembly, and then applying pressure to the assembly in the presence ofheat to directly adhere the greasy leads to a wood slat and the woodslats to each other.

'14. A method of making wood-encased lead pencils comprising applying awet coating of a vinyl resin within the grooves and upon the adjacentfiat areas of each of a pair of grooved wood slats, disposing greasyleads in one of the slats, assembling the other slat therewith, dryingthe coatings in the absence of pressure upon the assembly by highfrequency heating, and then applying pressure to the assembly in thepresence of heat to directly adhere the greasy leads to the wood slatsand the wood slats to each other.

15. A method of making wood-encased lead pencils as set forth in claim14, wherein the dry vinyl resin adhesive film on each of the slats isdeposited from an emulsion of plasticized polyvinyl acetate.

'16. A method of making wood-encased lead pencils as set forth in claim,14, wherein the substantially dry vinyl resin adhesive film on each ofthe slats is deposited from an emulsion of polyvinyl acetate plasticizedwith a ben- Zoic acid derivative in the proportions of approximately 80to 95 percent of the polyvinyl acetate and 5 to 20 percent of thebenzoic acid derivative, by weight.

17. A method of making wood-encased lead pencils as set forth in claim14, wherein pressure is applied to the assembly while the dried coatingsare still hot from the heat of drying.

Text on Adhesives: The Technology of Adhesives, by Del Monte, ReinholdPublishing Co., 330 W. 42nd St., New York 18, NY. (Copy in Division 60.)

1. A METHOD OF MAKING WOOD-ENCASED LEAD PENCILS COMPRISING PROVIDING ASUBSTANTIALLY DRY VINYL RESIN ADHESIVE FILM WITHIN THE GROOVES AND UPONTHE ADJACENT FLAT AREAS OF A GROOVED WOOD SLAT WHICH IS ASSEMBLED WITH ASECOND GROOVED SLAT AND WITH GREASY DISPOSED IN THE MATING GROOVES, ANDAPPLYING PRESSURE TO THE ASSEMBLY IN THE PRESENCE OF HEAT TO DIRECTLYADHERE THE GREASY LEADS TO A WOOD SLAT AND THE WOOD SLATS TO EACH OTHER.10. A METHOD OF MAKING WOOD-ENCASED LEAD PENCILS COMPRISING APPLYING AWET COATING OF A VINYL RESIN WITHIN THE GROOVES AND UPON THE ADJACENTFLAT AREAS OF EACH OF A PAIR OF GROOVED WOOD SLATS, APPLYING HEAT TO THECOATED SLATS TO FORM SUBSTANTIALLY DRY VINYL RESIN ADHESIVE FILM ON EACHOF THE SLATS AND, WHILE THE COATINGS ARE STILL HOT FROM THE HEAT OFDRYING, PLACING THE OTHER SLAT THEREON AND APPLYING PRESSURE TO THEASSEMBLY TO DIRECTLY ADHERE THE GREASY LEADS TO THE WOOD SLATS AND THEWOOD SLATS TO EACH OTHER.
 14. A METHOD OF MAKING WOOD-ENCASED LEADPENCILS COMPRISING APPLYING A WET COATING OF A VINYL RESIN WITHIN THEGROOVES AND UPON THE ADJACENT FLAT AREAS OF EACH OF A PAIR OF GROOVEDWOOD SLATS, DISPOSING GREASY LEADS IN ONE OF THE SLATS, ASSEMBLING THEOTHER SLAT THEREWITH, DRYING THE COATINGS IN THE ABSENCE OF PRESSUREUPON THE ASSEMBLY BY HIGH FREQUENCY HEATING, AND THEN APPLYING PRESSURETO THE ASSEMBLY IN THE PRESENCE OF HEAT TO DIRECTLY ADHERE THE GREASYLEADS TO THE WOOD SLATS AND THE WOOD SLATS TO EACH OTHER.